Blinds for building openings, eg windows, doors and the like, may be operated either simply down and up, in the case of eg. roller blinds, or in the case of eg. Venetian blinds or vertical shade panels, the shade panels may be rotated open or closed.
The control elements for these blind operations are usually in the form of an endless cord or chain. The control element simply hangs down along one side of the building opening, in an endless loop.
Other forms of blinds and window coverings may also be operated by means of an endless control element hanging in a loop.
In the past this system has been widely used, and experience has mainly been satisfactory. In some cases a pendant weight was located on the loop, to assist in controlling it.
In U.S. Pat. No. 8,539,645 Inventor Mario M. Marocco, there is shown an earlier form of lock for a blind cord loop in which a spring operated lock is used.
However building codes are now requiring that the endless loop type of control element shall be guided and controlled at its lower end. It should always be tensioned. The intent of this code is to prevent any chance that the element, when loose, may possibly create a hazard to children, or handicapped persons, or even pets.
In addition, by guiding and controlling the loop of the element at its lowest point, its operation by anyone becomes somewhat easier. The element is prevented from becoming twisted, or entangled with any other blinds controls, curtains or the like.
A simple pulley, fixed to the building fabric, and holding the loop in tension, would achieve this result, in most cases. However such a pulley may become dislodged or loosened from the building to which it was attached. The guide pulley will then hang loose on the loop of the element, leaving the element uncontrolled, as before.
In other cases the pulley might have been installed incorrectly.
In order to provide a more satisfactory form of cord guide, tension device systems have been developed in which the actual pulley wheel was held by a spring. When the guide was installed correctly, the spring pressure was applied through the pulley wheel to the control element thus holding the endless loop in tension. The control element could then be operated freely.
But if the guide became dislodged, or if the guide was installed incorrectly, the spring was released, the element was held locked by the mechanism in the guide. The blind could not then be operated.
This would alert the home owner to correct the problem, and have the guide reinstalled correctly.
Several such systems have been proposed, and are in use. However these prior systems have suffered from certain problems. In some there were several small loose parts of plastic. The installer had to be trained to assemble these correctly. If any of these parts became loose, they could create a health hazard. They might have been installed incorrectly. They might simply be missing, or lost.
Other systems have required great care in connecting the control element to the pulley, and then setting the spring to the correct tension.
Other systems were costly to manufacture, or might require several different forming dies, at considerable expense.